Many modern light trucks and passenger cars with diesel engines use high pressure distributor pumps for fuel injection. Such distributor pumps always include a transfer pump, frequently a vane pump, situated within the injection pump housing. The purpose of the transfer pump is to increase the fuel supply pressure to a level where it will adequately fill the distributor system, as well as operating other features of the injection pump, such as the timing control system. The transfer pump has a closed loop pressure regulating system that provides pressure as a function of rotational speed. The pressure typically ranges from 200 kPa at lower engine speeds to 850 kPa at higher engine speeds.
The transfer pump mounted within the fuel injection pump is frequently used to pull fuel from the fuel tank. Such a prior art system is shown in FIG. 9, in which fuel injection pump 80 has transfer pump 81 incorporated therein. Fuel drawn from tank 94 by pump 81 passes through supply line 98 and filter 92 before reaching pump 81. Because the fuel lines and components extending from fuel tank 94 to fuel injection pump 80 are at negative pressure, this is generally known as a "depression fuel system". Depression fuel systems are prone to problems caused by the negative pressure, which can cause air ingress through minor leaks, resulting in unstable fuel injection and even failure of the engine to start. For this reason, more reliable vehicles with diesel engines have also included a primary or lift pump, to cause the fuel system to always operate at a positive pressure, preventing air ingress. If air or vapor does get into the fuel line between the fuel tank and the primary pump, a continuous bleed located in the pressurized part of the system will send the vapor and air back to the fuel tank.
Primary pumps used with diesel injection systems typically comprise a camshaft driven, self-regulating, reciprocating diaphragm type pump. However, on newer diesel engines with one or more overhead camshafts, the diaphragm pump becomes difficult to package. Also, the diaphragm fuel pump may not have adequate fuel flow for cooling modern high pressure distributor pump with electronic controls and spill type metering systems. Although diaphragm pumps are being replaced with electrically driven primary pump systems, this arrangement is not entirely satisfactory because electric pumps are expensive and require a separate dedicated pressure regulator. And, electric lift pumps suffer from a drawback inasmuch as they operate at essentially a constant volume which must be sized so as to exceed engine requirements at low speeds, while providing marginal fueling at higher speeds.
The present invention provides a reliable, low cost primary fuel pump. This pump can be used at minor added cost to change depression fuel systems to pressurized fuel systems, improving the reliability. The present low cost pump can also be used to replace electrically driven pumps in pressurized fuel systems, reducing the system cost.